The invention relates to a universal object holder for plate-shaped objects of differing dimensioning for use on a microscope.
In the production of chips, specially coordinated reflected-light/transmitted-light microscope arrangements are used under clean-room conditions in order to observe wafers or masks and to obtain an overview of occurring defects. If now, on cost grounds, the use of fully automatic inspection microscopes is dispensed with, or if the numbers of units involved are small, then the individual wafers or masks must be inserted into the microscope manually. In this case, there is the danger that the fragile wafers or masks will be damaged by the conventional clamping devices secured to the microscope stage. Furthermore, the holding or clamping devices must be designed to be abrasion-resistant and free from gas-liberating lubricants or lacquers.
Holding devices which satisfy these conditions are already known and consist essentially of a frame which is mounted on a microscope stage. By means of individual prefabricated rings, which can be inserted into this frame and which have differing dimensions, a defined mounting for the most widely varying mask sizes may be achieved. The exchange of the masks or wafers can take place from above, in which case these contact the bearing surface only by their edge regions. However, a disadvantage is represented by the multiplicity of the required rings in order to retain the currently known sizes and shapes. Masks or wafers are protected by this holding device only against a lateral sliding, since a definitive securing of the wafer or of the masks is not possible. Accordingly, it has proved to be an advantage to retain such sensitive objects by means of a vacuum device.
Such an object holder is known from DE-OS No. 3,321,853, and consists essentially of a U-shaped body part, the bottom of which is equipped with a plane contact surface. Furthermore, pinshaped abutments for the positioning of slides are fitted into the bottom. In the contact surface, air sucking-in openings are provided, which are connected to a channel within the body part. A reduced pressure may be generated in this channel by means of a vacuum pump so that the slides are pressed against the force of gravity onto the contact surface.
However, this object holder exhibits the disadvantage that it may be used only for slides of a definite shape and size. Furthermore, the objects must be placed in position from below. However, such a retention does not enter into consideration for objects with highly sensitive surfaces.
A further object holder is known from DE-PS No. 2,449,291. Two upright base bodies are disposed with respective arms opposite one another on a stage. These arms exhibit a plane slide-directing surface, which points in the direction of the stage. Furthermore, the slide-directing surfaces are equipped with openings, which are connected to vacuum lines. The air is evacuated by means of an appropriate pump, and the slide is held against the force of gravity by the reduced pressure.
This object holder also accepts only slides of a specified size and shape, and, in addition, exhibits the disadvantage that the sensitive surface of a wafer is pressed against a contact surface.
U.S.-PS No. 4,557,568 discloses an object holder for the mounting of masks with and without a pellicle frame of differing size. To this end, this object holder exhibits a rectangular frame, with which two mutually opposite strips each having a respective bearing surface are associated. These strips are connected to the frame by means of screws or can be displaced relative to one another by means of drive means. In the strips a plurality of bores are present into which pins are introduced in order to secure the objects against a lateral displacement. Accordingly, this object holder can be adapted to the most widely varying dimensions of rectangular masks. However, it is a disadvantage that only two bearing surfaces are provided, and accordingly the danger of bowing exists in the case of large masks. As a result of the pins, especially round masks may only inadequately be secured against a lateral displacement, it being possible for the exchange of masks to take place only by exact vertical feed or removal.
The foregoing illustrates limitations known to exist in present devices. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.